Mobile and Wireless Network Investigation

Running head: MOBILE AND WIRELESS NETWORK INVESTIGATION
Mobile and Wireless Network Investigation
Name of the Student
Name of the University
Author Note

MOBILE AND WIRELESS NETWORK INVESTIGATION
1
Part - A
Question 1: Accessing Wireless Network
a) What is media access control and why is it important?
MAC or Media Access Control determines when the nodes get approval for
transmitting their packets, as also to control all kinds of access to physical layer in general.
Particular functions that are associated with the MAC protocol can vary based on system
requirements and the applications being used. Data streams are carried by wireless networks
with strict QoS or quality of service requirements. This involves general concepts such as a
MAC protocol that is complex enough to manage bandwidth resources adaptively so as to
meet the network demands.
b) Give one example each of the controlled access methods and contention based media
access methods?
A major example of controlled access method is Polling. Based on this method
servers repeatedly contact clients to check if they are willing to transmit. The clients on the
other hand will only transmit once the server asks them if they wishes to send anything.
One key example of contention based media access control is CSMA/CA. Among the
LAN protocols, wireless or WLAN is a widely used and a fast growing one. The mechanism
to resolve contention problems in 802.11 wireless networks is CSMA/CA or collision
avoidance. Here the media gets evaluated by the device to check for existence of data signals.
When the media becomes free, a notification is sent by the device alerting the media of the
intention to use that.
c) When might one access method be preferred over another in a network, and why?
The response time of contention based media access control is significantly better
compared to that of controlled access methods when the traffic is low. However when the

MOBILE AND WIRELESS NETWORK INVESTIGATION
2
traffic scales higher, the response time worsens versus controlled access methods
dramatically. As a result, contention based media access control is considered ideal for
smaller sized networks and controlled access methods should be chosen for larger networks
with more traffic.
d) Under what conditions do contention-based media access control techniques
outperform controlled-access techniques (i.e., have lower response time)? Explain
Contention based media access control works in opposite ways in respect to
controlled access. Here computers are to wait till circuit becomes free and transmits when
data is to be sent. Generally contention based approaches perform well versus controlled
access in smaller networks with lower usage. The low usage results in fewer chances of
collisions. In comparison, devices under controlled access have to wait to acquire permissions
that is even when other computers are not transmitting, the devices have to wait for polling.
For large networks with high usage the opposite applies. Here controlled access works
better as in high volume networks, numerous computers require transmission, and probability
of collisions with contention is significant. These collisions directly affect throughput by
wasting circuit capacity in collisions requiring retransmission from the computers afterwards.
Collisions are prevented by controlled access as it uses the circuit more efficiently and hence
the increase in response times is gradual.
Question 2: Four Users (U1, U2, U3 and U4) are using CDMA access techniques
to transmit data to their respective receivers (U1->R1, U2->R2, U3->R3 and U4-
>R4). The followings are the spreading codes and the data that each user wants
to send.
Users Spreading Code Data to send
U1 1111 000